A cruise controller may be installed on a machine in order to allow an operator to set a desired cruising speed of the machine. Various cruise control systems are known in the art. For example, U.S. Pat. No. 5,495,251 discloses a vehicle cruise controller which monitors the range to and relative speed of a target vehicle ahead of the vehicle being controlled by the cruise controller. A radar provides measurements of range and relative speed. The range measurement is compared by a subtracter with a desired range which is a function of vehicle speed, so as to form a distance error. The relative speed signal represents a speed error. An acceleration demand is formed as a function, for example a weighted sum, of the distance and speed errors. The acceleration demand may be supplied to vehicle brake and drive systems, but preferably the acceleration demand is compared with actual vehicle acceleration to provide the advantages of closed loop control.